I am taking measurements off the screen of an analog oscilloscope in order to calculate voltage and frequency of a sinusoidal wave form. The volts per division is set to 0.50V, and the time per division is set to 0.50 ms. I measure the vertical length of the trace to be 2.67 divisions. I measure the horizontal length of the trace to be 0.87 divisions. I will assume that I can estimate my measurement to within 1/100 of a division. Now I must do the following calculations to get the voltage and period of the wave form: 2.67 divisions * 0.50 V = 1.335 V 0.87 divisions * 0.50 ms = 0.435 ms According to rules of significant figures, my answers should be rounded to 1.34 V and 0.44 ms. Why is the zero in 0.87 ignored as a significant figure? I know for a fact that my estimated measurement of 0.87 is not 1.87, not 2.87, not 3.87, etc. It doesn't make sense to me that I keep 3 significant figures for the measured voltage and only 2 significant figures for the measured period when both measurements are being measured using the same device-the division tick marks on the screen of the oscilloscope.